The Genometric Analysis Simulation Program (G.A.S.P.) is a software tool for generating samples of family data based on user-specified genetic models. Quantitative traits are defined in terms of a combination of user-defined components, including a major-locus (or loci), a polygenic component, common sibship environment, and/or other covariates. In addition, loci corresponding to discrete traits or markers can be generated. However, complications such as missing data, genotyping errors reduced penetrance, genetic heterogeneity, epistasis, and non-random ascertainment of samples are not handled directly by this software. G.A.S.P. is run in combination with a drevier which formats the generated data and can also be used to add layers of complexity to the model. Simple examples of driver-added traits modifications include: classification of a quantitative trait into a discrete trait using a specific threshold, suppressing (as unknown) genotyping data for older generations of a family and reduced penetrance for a qualitative trait. The software is being used extensively in the Inherited Disease Research Branch, and has been requested by over 40 investigators worldwide. During the past year, the software was used extensively in the development of a new method for testing association for quantitative traits (ROMP), comparing the statistical properties of tests of association (ROMP, ANOVA, Variance components), and comparing the statistical properties of linkage analysis.